Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$19.73	5.848%	$20.8838	$20.88	$20.90	$20.90
Purchase #2	$241.69	3.495%	$250.1371	$250.14	$250.15	$250.10
Purchase #3	$205.60	5.741%	$217.4035	$217.40	$217.40	$217.40
Purchase #4	$238.35	4.215%	$248.3965	$248.40	$248.40	$248.40
Purchase #5	$34.48	13.728%	$39.2134	$39.21	$39.20	$39.20
Purchase #6	$70.58	7.779%	$76.0704	$76.07	$76.05	$76.10
Purchase #7	$186.25	6.578%	$198.5015	$198.50	$198.50	$198.50
7 purchase totals =	$996.68		$1,050.6062	$1,050.60	$1,050.60	$1,050.60